"Drop foot" is a frequently encountered condition in which a person is unable to lift a foot. Drop foot may be the result of nerve damage from spinal surgery, brain damage from cardiovascular accident (CVA) or "stroke", hereditary motor and sensory neuropathies, or neuromuscular disease, such as Dystrophia Myotonica. Any damage to the "motor unit" (i.e., muscle and nerves which activate the muscle) of the neuromuscular system related to the foot may cause drop foot.
The neuromuscular system of the foot comprises the pretibial muscles which are those muscles on the front of the leg and below the knee which lift the foot. The action of lifting the foot from a position substantially aligned with the lower leg to a position substantially perpendicular to the lower leg is known by the term "dorsiflexion." However, if the pretibial muscles are weak, a person will be unable to lift the foot as required in the swing phase of a gait. This inability to lift the foot may cause a person to trip, since the foot may make contact with the grounds during the downward swing of the leg.
A person may avoid having the foot contact the ground by lifting the entire leg higher, but this is not efficient in terms of energy expenditure. Another solution is to use a brace to mechanically lift the foot and give the person a more stable, energy efficient gait. This type of brace or "orthosis" is known as an Ankle-Foot Orthosis (AFO). Prior art AFO's comprise double metal uprights attached to the shoe or a thermoplastic rigid 90.degree. brace made to fit inside of a shoe.
Drop foot may have other side effects such as a loss or diminishing of the sensation of touch. The sensation of touch includes the ability to feel a pin prick or pain and the ability to sense movement. Kinesthesia is the ability to sense the movement of muscles, tendons, and joints. In particular, proprioceptors are special receptor nerves which enable one to sense the movement of muscles, tendons, and joints. The proprioceptors are located in the subcutaneous tissue of the muscles, tendons, and joints and they respond to stimuli produced within the body. The proprioceptors allow one to know where one's foot or hand is in space without seeing them.
A human body relies on three systems for maintaining balance: the vestibular system, the visual system, and the somatic-sensory system or kinesthesia. It is possible to maintain balance with only two of the systems in operation. In the case of a foot, the foot normally contacts the floor and the three most important areas are: 1) the first metatarsal head; 2) the fifth metatarsal head; and 3) the calcaneus or heel. These three contact areas form a tripod in which the foot is supported and in which sensory feed-back is provided to maintain balance.
However, when drop foot causes a loss or reduction of kinesthesia, a person using prior art AFO's may only be able to maintain balance during a walk by looking at his or her feet. This is so because the prior art AFO's impose an extra barrier between the foot and the floor causing a decrease in kinesthesia.
Accordingly, it is an object of the present invention to provide an orthosis which provides improved kinesthesia for a wearer of an AFO.
It is another object of the present invention to provide an orthosis which may enable the wearer to reduce his or her dependence on walking aids for balance, such as canes or walkers.
It is another object of the present invention to produce a more stable gait and a more energy efficient gait during walking.